While the moon’s influence on the timing and amplitude of ocean waves is well known, a team of researchers from the University of Washington has discovered that lunar position also creates slight, nearly imperceptible changes in precipitation amounts here on Earth.
As corresponding author Tsubasa Kohyama, a doctoral student in atmospheric sciences, and co-author/UW professor John M. Wallace reported in Saturday’s edition of the journal Geophysical Research Letters, when the moon is high in the sky, it produces forces that create bulges in the atmosphere, affecting the amount of rain received by the planet below.
“As far as I know, this is the first study to convincingly connect the tidal force of the moon with rainfall,” said Kohyama, who was studying atmospheric waves when he first discovered a minor oscillation in air pressure correlating to the phases of the moon. After two years of work, he and Wallace concluded “when the moon is overhead or underfoot, the air pressure is higher.”
High moon increases atmospheric pressure, lowers relative humidity
In instances where the moon is overhead, its gravity causes the Earth’s atmosphere to bulge in its direction, resulting in a atmospheric weight or pressure increase on that side of the planet. Higher pressure increases the temperature of air parcels below, the authors explained, which enables this now-warmer air to hold more moisture.
“It’s like the container becomes larger at higher pressure,” Kohyama explained. Rainfall amounts are affected by relative humidity because “lower humidity is less favorable for precipitation,” the UW student added. This means that when the moon is high, less precipitation will fall.
However, those changes are relatively minute, with rainfall variation of only about one percent. As Kohyama said, “No one should carry an umbrella just because the moon is rising.” Rather, he and Wallace suggest that their research could be used to help test climate models, making certain that their physics can adequately simulate how the moon’s pull can result in less rain.
Their conclusions came following an extensive review of 15 years worth of data collected by the NASA and Japan Aerospace Exploration Agency’s Tropical Rainfall Measuring Mission satellite between 1998 and 2012. Wallace said that he plans to continue looking at the data, searching for possible connections between the moon and other types of precipitation, such as downpours, and to see it lunar forces have any influence on rainstorm frequency.
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Feature Image: Thinkstock
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